TIME NECESSARY. 159 



cessive tertiary periods, during which the Flora 

 and Fauna of the globe have been almost entirely 

 changed ! Yet how subordinate a place in the long 

 calendar of geological chronology do the succes- 

 sive tertiary periods themselves occupy ! How 

 much more enormous a duration must we assign 

 to many antecedent revolutions of the earth and 

 its inhabitants ! No analogy can be found in the 

 natm-al world to the immense scale of these divi- 

 sions of past time, unless we contemplate the 

 celestial spaces, which have been measured by the 

 astronomer. Some of the nearest of these within 

 the limits of the solar system, as, for example, the 

 orbits of the planets, are reckoned by hundreds 

 of millions of miles, which the imagination in vain 

 endeavours to grasp. Yet one of these spaces, 

 such as the diameter of the earth's orbit, is re- 

 garded as a mere unit, a mere infinitesimal fraction 

 of the distance which separates our sun from the 

 nearest star. By pursuing still further the same 

 investigations, we learn that there are Imninous 

 clouds, scarcely distinguishable by the naked eye, 

 but resolvable by the telescope into clusters of 

 stars, which are so much more remote, that the 

 interval between our sun and Sirius may be but a 

 fraction of this larger distance. To regions of 



